Ozone levels above the mid-southern hemisphere dropped 13 per cent after Australia’s worst fires on record due to chemical reactions triggered by the smoke
Australia’s record-breaking wildfires of 2019 and 2020 blasted smoke so high that even the ozone layer in the stratosphere was damaged, a new analysis shows.
The Black Summer bushfires, which raged along Australia’s east coast from November 2019 to January 2020, caused unprecedented destruction.
The fires burned more than 70,000 square kilometres of bushland, destroyed more than 3000 homes, and killed more than 30 people and billions of animals. Smoke billowed all the way to South America and triggered distant ocean algal blooms.
Now, Peter Bernath at Old Dominion University in Virginia and his colleagues have shown that the smoke also pushed its way up into the stratosphere and triggered chemical reactions that destroyed ozone.
They analysed data from the Atmospheric Chemistry Experiment satellite, which monitors levels of 44 different molecules in the atmosphere.
This revealed that stratospheric ozone declined by 13 per cent in the middle latitude area of the southern hemisphere – which includes Australia – in the aftermath of the Black Summer fires.
This appeared to be because the smoke broke into the stratosphere and interacted with chlorine-containing chemicals left over from our past widespread use of chlorofluorocarbons. The smoke converted these chemicals into forms that are highly destructive towards ozone, for example, chlorine monoxide and hypochlorous acid.
Wildfire smoke doesn’t normally make it into the stratosphere, but the Black Summer fires were so ferocious that they generated their own storm clouds – called pyrocumulonimbus clouds – that “punched the smoke into the stratosphere”, says Bernath.
A separate study by researchers at Jinan University in China showed that this smoke injection also warmed the stratosphere above the southern hemisphere by 1°C for six months after the fires.
Bernath and his colleagues found that the drop in stratospheric ozone caused by the fires lasted until December 2020 before returning to normal levels.
Megafires in Australia and other places such as California are expected to become more common as climate change takes hold, meaning more assaults on the ozone layer, which protects us from ultraviolet radiation, says Bernath. “As severe wildfires rise in number, they will play an increasingly important role in the global ozone budget,” he says.
Journal reference: Science, DOI: 10.1126/science.abm5611
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